1. Field of the Invention
This invention generally relates to the field of the transport of fluids, and in particular to the transport of polluting or even hazardous fluids which need to be kept out of the surrounding environment. More specifically, the present invention is concerned with the field of offshore oil exploration, and the tubes used for transporting the oil from an offshore oil platform to a distant loading area.
2. Background Information
The invention relates in particular to the flexible tubes used to establish high-capacity connections between loading or unloading points for petroleum products and tanker vessels. Flexible tubes used for such transport of petroleum products are subjected to mechanical fatigue stresses on account of the ocean swells and the movements of the vessels, that is any relative movement between the oil platform and the vessel being loaded. Such stresses are exacerbated by the aging which results from their continuous use in a marine environment.
In essence, over time, a problem therefore arises as to when such an oil carrying hose will rupture and allow oil to escape into the surrounding seawater. One remedy for such risks has therefore been directed to establishing a system for the visual detection of a failure within the hose before the hose actually ruptures, so that the hose can be replaced as quickly as possible. In this direction, it has therefore been proposed that a secondary reinforcement be installed along a portion of the length of the flexible hose, which secondary reinforcement can intervene in the event of a failure of the principal reinforcement. The secondary reinforcement can then be configured in a manner which visually shows that a rupture has occurred in the primary layer.
Such a solution is disclosed in French Patent No. 2 524 116 (Dunlop), which corresponds to U.S. Pat. No. 4,509,558. This solution teaches that in the event of a failure of the principal reinforcement, the pressure of the fluid being transported causes a localized radial swelling of the secondary reinforcement due to the elongation of the material of the secondary reinforcement. Such swellings make it possible to detect the failing hose by means of a visual inspection, before any ruptures occur, and thus preventing any leakage into the surrounding environment. Nevertheless, the desired effect of the localized deformation of the secondary reinforcement in this proposed solution is not altogether satisfactory.
In the solution proposed by Dunlop, when the secondary reinforcement is elongated, the resulting radial expansion is proportional to the leak pressure of the fluid. Thus, if the leak pressure is only a fraction of the operating pressure, such as might be the case for a relatively small leak, i.e., a small hole in the primary reinforcement, the resulting radial expansion is only a fraction of the maximum expansion, and therefore it becomes more difficult to detect a failure if the failure is relatively minor. The proposed measure is therefore effective only if the leak pressure is close to the operating pressure, such as might be the case for relatively large leaks, i.e., large holes or ruptures of the primary reinforcement, so that the radial expansion is close to the maximum value.
Another factor which reduces the benefit of such a known solution is that the radial expansion of the hose entails a corresponding reduction in the length of the hose. This reduction in length therefore means that it is necessary to use hoses which are longer than the distance between the elements to be connected, so that if a rupture were to occur the radial expansion and corresponding length reduction would not make the hose too short for use.
The present invention therefore relates to a flexible hose having two coaxial reinforcements, the outermost of which is designated as a safety reinforcement and essentially provides the confinement of any fluid which may have leaked through the failed principal reinforcement, wherein a set of localized deformations of the flexible hose makes it possible to identify a leakage in the hose by a visual inspection of the outside of the hose.